Nikon D6 Reference Manual page 1132

5
Remove any dust and lint from
the low-pass filter with a
blower.
•
Do not use a blower-brush. The
bristles could damage the filter.
•
Dirt that cannot be removed with a
blower can only be removed by Nikon-authorized service
personnel. Under no circumstances should you touch or
wipe the filter.
6
Turn the camera off and replace the lens.
The mirror will return to the down position and the shutter
curtain will close.
1080 Caring for the Camera